1. Field of Invention
This invention relates to improving the efficiency of automatic transmissions used in motor vehicles.
2. Prior Art
There have been a number of inventions in the history of vehicle transmissions. Ford's famous Model A used a 3 speed manual transmission and a foot operated clutch. This transmission changed gear ratios by sliding different gears into engagement. There was no automatic method for insuring that the gears were turning at a matching speed as they were engaged. This required the driver to carefully synchronize the speed of the gears before shifting. Failure to do this well would result in grind the gears and a shorter transmission life. A driver had to learn a complicated process called double clutching. This entailed pressing the clutch pedal two times while at the same time changing engine speed to bring the gears into synchronization.
This was difficult for most people to master. The solution was a transmission with automatic synchronizers. This eliminated the need for double clutching. The synchronizers acted between the gears to eliminate any speed difference. Thus, the transmission could be shifted without worrying about grinding gears.
In a synchromesh transmission all gears were engaged at all times, a feature called constant mesh. The transmissions gear ratio is changed by using shifter rings that lock the desired gear to its shaft. This design combines two features; constant mesh gears and synchronizers. All modern standard transmission cars have synchromesh transmissions.
Unfortunately, in a constant mesh transmission all gears remain engaged and turning even when not carrying the load thereby causing drag and reducing energy efficiency. Furthermore, the synchronizer rings for those gears not engaged also cause drag wasting more power and additional reductions in efficiency.
But people did not want to worry about shifting at all. Thus was born the fully automatic transmission. This removed the chore of shifting the transmission completely. Gear changes were entirely managed by engaging clutches which were controlled by a computer.
Early designs had a hydraulic computer that controlled the clutches. More recently, the management of the transmission is left to an electronic computer. Automatic transmissions are also constant mesh gearboxes but are shifted by means of friction clutches. The transmission has series of clutches that allow a particular set of planetary gears to rotate or to be locked together.
In any particular gear some clutches would be engaged and others would be relaxed. The relaxed clutches also spin resulting in drag which reduces efficiency.
Each of these inventions solved some problems but exacerbated other problems. The Model A transmission was simple and very efficient. No gears were engaged unless they were being used to carry power. This reduced friction and wear. However, it was difficult to use and gears could be damaged by improper shifting.
The synchromesh transmission was much easier to use but had many moving parts all contributing to drag. All gears were engaged at all times with only some of the gears being used to carry power. The synchronizer clutches dragged for all the gears except the one currently selected.
The fully automatic transmission was even easier to use but had even more moving parts all contributing to wear and drag. In any particular gear, multiple clutches would not be engaged but were rotating thereby adding to drag.